Mixed signals in heart failure: cancer rules

Decrease of Pdzrn3 is required for heart maturation and protects against heart failure

Heart failure is the final common stage of most cardiopathies. Cardiomyocytes (CM) connect with others via their extremities by intercalated disk protein complexes. This planar and directional organization of myocytes is crucial for mechanical coupling and anisotropic conduction of the electric signal in the heart. One of the hallmarks of heart failure is alterations in the contact sites between CM. Yet no factor on its own is known to coordinate CM polarized organization. We have previously shown that PDZRN3, an ubiquitine ligase E3 expressed in various tissues including the heart, mediates a branch of the Planar cell polarity (PCP) signaling involved in tissue patterning, instructing cell polarity and cell polar organization within a tissue. PDZRN3 is expressed in the embryonic mouse heart then its expression dropped significantly postnatally corresponding with heart maturation and CM polarized elongation. A moderate CM overexpression of Pdzrn3 (Pdzrn3 OE) during the first week of life, induced a severe eccentric hypertrophic phenotype with heart failure. In models of pressure-overload stress heart failure, CM-specific Pdzrn3 knockout showed complete protection against degradation of heart function. We reported that Pdzrn3 signaling induced PKC ζ expression, c-Jun nuclear translocation and a reduced nuclear ß catenin level, consistent markers of the planar non-canonical Wnt signaling in CM. We then show that subcellular localization (intercalated disk) of junction proteins as Cx43, ZO1 and Desmoglein 2 was altered in Pdzrn3 OE mice, which provides a molecular explanation for impaired CM polarization in these mice. Our results reveal a novel signaling pathway that controls a genetic program essential for heart maturation and maintenance of overall geometry, as well as the contractile function of CM, and implicates PDZRN3 as a potential therapeutic target for the prevention of human heart failure.

The MEK/ERK Module Is Reprogrammed in Remodeling Adult Cardiomyocytes

Fetal and hypertrophic remodeling are hallmarks of cardiac restructuring leading chronically to heart failure. Since the Ras/Raf/MEK/ERK cascade (MAPK) is involved in the development of heart failure, we hypothesized, first, that fetal remodeling is different from hypertrophy and, second, that remodeling of the MAPK occurs. To test our hypothesis, we analyzed models of cultured adult rat cardiomyocytes as well as investigated myocytes in the failing human myocardium by western blot and confocal microscopy. Fetal remodeling was induced through endothelial morphogens and monitored by the reexpression of Acta2, Actn1, and Actb. Serum-induced hypertrophy was determined by increased surface size and protein content of cardiomyocytes. Serum and morphogens caused reprogramming of Ras/Raf/MEK/ERK. In both models H-Ras, N-Ras, Rap2, B- and C-Raf, MEK1/2 as well as ERK1/2 increased while K-Ras was downregulated. Atrophy, MAPK-dependent ischemic resistance, loss of A-Raf, and reexpression of Rap1 and Erk3 highlighted fetal remodeling, while A-Raf accumulation marked hypertrophy. The knock-down of B-Raf by siRNA reduced MAPK activation and fetal reprogramming. In conclusion, we demonstrate that fetal and hypertrophic remodeling are independent processes and involve reprogramming of the MAPK.

Differentially expressed lnc-NOS2P3-miR-939-5p axis in chronic heart failure inhibits myocardial and endothelial cells apoptosis via iNOS/TNFα pathway

Inflammatory cytokine‐induced cell apoptosis is important for initiation and progression of chronic heart failure (CHF). Non‐coding RNAs, including long non‐coding RNAs and microRNAs, have emerged as critical regulators of this pathological process. The role in regulating inflammation and induction to cell apoptosis in CHF is not well understood. This study found CHF patients had elevated serum miR‐939‐5p, with greater increase in New York Heart Association (NYHA) I‐II patients than in NYHA III‐IV. Moreover, miR‐939‐5p was positively correlated with B‐type natriuretic peptide (BNP) in NYHA III‐IV patients, while not in NYHA I‐II. Further study showed miR‐939‐5p mimics promoted cell proliferation and inhibited inflammatory cytokine‐induced apoptosis of HUVECs and H9C2, while inhibition of endogenous miR‐939‐5p produced the opposite effects. Induced nitric oxide synthase (iNOS) and tumour necrosis factor α (TNFα) were identified as target genes of miR‐939‐5p. Additionally, lncRNA‐NOS2P3 acted as an endogenous sponge RNA to inhibit miR‐939‐5p expression, regulate the expression of iNOS/TNFα and control inflammation‐induced cells apoptosis. These suggest that CHF patients exhibited elevated serum miR‐939‐5p level especially in NYHA I‐II grades. And lnc‐NOS2P3‐miR‐939‐5p‐iNOS/TNFα pathway regulated inflammatory cytokine‐induced endothelial and myocardial cells apoptosis and provided a promising strategy for diagnosis and treatment of CHF.

The role of stretch, tachycardia and sodium-calcium exchanger in induction of early cardiac remodelling

Stretch and tachycardia are common triggers for cardiac remodelling in various conditions, but a comparative characterization of their role in the excitation‐transcription coupling (ETC) and early regulation of gene expression and structural changes is lacking. Here, we show that stretch and tachycardia directly induced hypertrophy of neonatal rat cardiac myocytes and also of non‐myocytes. Both triggers induced similar patterns of hypertrophy but had largely distinct gene expression profiles. ACTA1 served as good hypertrophy marker upon stretch, while RCAN1 was found increased in response to tachycardia in a rate‐dependent fashion. Mechanistically, several calcium‐handling proteins, including the sodium‐calcium exchanger (NCX), contributed to ETC. Phosphorylation of the calcium/calmodulin‐dependent protein kinase II (CaMKII) was elevated and occurred downstream of NCX activation upon tachycardia, but not stretch. Microarray profiling revealed that stretch and tachycardia regulated around 33% and 20% genes in a NCX‐dependent manner, respectively. In conclusion, our data show that hypertrophy induction by stretch and tachycardia is associated with different gene expression profiles with a significant contribution of the NCX.

Residual congestion and long-term prognosis in acutely decompensated heart failure patients

AIMS

Recent studies have established the role of residual congestion evaluated by lung ultrasound in estimating short-term risk of readmission or death in patients admitted for heart failure (HF) decompensation. However, if lung ultrasounds maintain a prognostic role of in long-term survival is still unknown. Aim of our study was to evaluate if residual congestion could predict all-cause mortality during 4 year follow up in a cohort of unselected patients admitted for acute decompensated HF.

METHODS

One-hundred fifty patients were enrolled. The anterolateral chest was scanned to evaluate the presence of B-lines. A sonographic score was calculated attributing 1 to each positive sector (≥ 3 B-lines). Clinical, biochemical and echocardiographic data were recorded. A Cox proportional hazard regression analysis was performed to evaluate the association between variables and 4-year survival.

RESULTS

During the follow-up, 86 patients (58%) died. Univariate analysis showed a significant correlation between the sonographic score at discharge and events occurrence at long term follow up (HR 1.21; CI 1.11-1.31; p < 0.001) suggesting that, on average, the increase of 1 point in the sonographic score was associated with an increase of approximately 20% in the risk of death.

CONCLUSIONS

Our results suggest the role of LUS in the identification of more congested HF patients, that will be at risk for worse long term outcome.

Phosphodiesterase 9a Inhibition in Mouse Models of Diastolic Dysfunction

BACKGROUND

Low myocardial cGMP-PKG (cyclic guanosine monophosphate-protein kinase G) activity has been associated with increased cardiomyocyte diastolic stiffness in heart failure with preserved ejection fraction. Cyclic guanosine monophosphate is mainly hydrolyzed by PDE (phosphodiesterases) 5a and 9a. Importantly, PDE9a expression has been reported to be upregulated in human heart failure with preserved ejection fraction myocardium and chronic administration of a PDE9a inhibitor reverses preestablished cardiac hypertrophy and systolic dysfunction in mice subjected to transverse aortic constriction (TAC). We hypothesized that inhibiting PDE9a activity ameliorates diastolic dysfunction.

METHODS

To examine the effect of chronic PDE9a inhibition, 2 diastolic dysfunction mouse models were studied: (1) TAC-deoxycorticosterone acetate and (2) Lepr^db/db. PDE9a inhibitor (5 and 8 mg/kg per day) was administered to the mice via subcutaneously implanted osmotic minipumps for 28 days. The effect of acute PDE9a inhibition was investigated in intact cardiomyocytes isolated from TAC-deoxycorticosterone acetate mice. Atrial natriuretic peptide together with PDE9a inhibitor were administered to the isolated intact cardiomyocytes through the cell perfusate.

RESULTS

For acute inhibition, no cellular stiffness reduction was found, whereas chronic PDE9a inhibition resulted in reduced left ventricular chamber stiffness in TAC-deoxycorticosterone acetate, but not in Lepr^db/db mice. Passive cardiomyocyte stiffness was reduced by chronic PDE9a inhibition, with no differences in myocardial fibrosis or cardiac morphometry. PDE9a inhibition increased the ventricular-arterial coupling ratio, reflecting impaired systolic function.

CONCLUSIONS

Chronic PDE9a inhibition lowers left ventricular chamber stiffness in TAC-deoxycorticosterone acetate mice. However, the usefulness of PDE9a inhibition to treat high-diastolic stiffness may be limited as the required PDE9a inhibitor dose also impairs systolic function, observed as a decline in ventricular-arterial coordination, in this model.

The Anti-Cancer Multikinase Inhibitor Sorafenib Impairs Cardiac Contractility by Reducing Phospholamban Phosphorylation and Sarcoplasmic Calcium Transients

Tyrosine-kinase inhibitors (TKIs) have revolutionized cancer therapy in recent years. Although more targeted than conventional chemotherapy, TKIs exhibit substantial cardiotoxicity, often manifesting as hypertension or heart failure. Here, we assessed myocyte intrinsic cardiotoxic effects of the TKI sorafenib and investigated underlying alterations of myocyte calcium homeostasis. We found that sorafenib reversibly decreased developed force in auxotonically contracting human myocardia (3 µM: -25 ± 4%, 10 µM: -29 ± 7%, 30 µM: -43 ± 12%, p < 0.01), reduced peak cytosolic calcium concentrations in isolated cardiomyocytes (10 µM: 52 ± 8.1% of baseline, p < 0.001), and slowed cytosolic calcium removal kinetics (RT50, RT10, Tau, p < 0.05). Beta-adrenergic stimulation induced augmentation of calcium transient (CaT) amplitude was attenuated in sorafenib-treated cells (2.7 ± 0.3-fold vs. 3.6 ± 0.2-fold in controls, p < 0.001). Sarcoplasmic reticulum (SR) calcium content was reduced to 67 ± 4% (p < 0.01), and SR calcium re-uptake slowed (p < 0.05). Sorafenib significantly reduced serine 16 phosphorylation of phospholamban (PLN, p < 0.05), while PLN threonine 17 and CaMKII (T286) phosphorylation were not altered. Our data demonstrate that sorafenib acutely impairs cardiac contractility by reducing S16 PLN phosphorylation, leading to reduced SR calcium content, CaT amplitude, and slowed cytosolic calcium removal. These results indicate myocyte intrinsic cardiotoxicity irrespective of effects on the vasculature and chronic cardiac remodeling.

Mechanical stretch induced transcriptomic profiles in cardiac myocytes

Mechanical forces are able to activate hypertrophic growth of cardiomyocytes in the overloaded myocardium. However, the transcriptional profiles triggered by mechanical stretch in cardiac myocytes are not fully understood. Here, we performed the first genome-wide time series study of gene expression changes in stretched cultured neonatal rat ventricular myocytes (NRVM)s, resulting in 205, 579, 737, 621, and 1542 differentially expressed (>2-fold, P < 0.05) genes in response to 1, 4, 12, 24, and 48 hours of cyclic mechanical stretch. We used Ingenuity Pathway Analysis to predict functional pathways and upstream regulators of differentially expressed genes in order to identify regulatory networks that may lead to mechanical stretch induced hypertrophic growth of cardiomyocytes. We also performed micro (miRNA) expression profiling of stretched NRVMs, and identified that a total of 8 and 87 miRNAs were significantly (P < 0.05) altered by 1-12 and 24-48 hours of mechanical stretch, respectively. Finally, through integration of miRNA and mRNA data, we predicted the miRNAs that regulate mRNAs potentially leading to the hypertrophic growth induced by mechanical stretch. These analyses predicted nuclear factor-like 2 (Nrf2) and interferon regulatory transcription factors as well as the let-7 family of miRNAs as playing roles in the regulation of stretch-regulated genes in cardiomyocytes.

miR199a-3p regulates P53 by targeting CABLES1 in mouse cardiac c-kit+ cells to promote proliferation and inhibit apoptosis through a negative feedback loop

Background

MicroRNAs (miRNAs) have emerged as crucial factors that regulate proliferation and apoptosis of cardiac c-kit⁺ cells. Although much is known about their role in maintaining cardiac c-kit⁺ cell pluripotency, the mechanisms by which they affect cell fate decisions that are an essential part of the repair of heart failure remain poorly understood.

Methods

Cardiac c-kit⁺ cells were obtained from Balb/c mice and cultured in vitro. Lentiviral vectors of miR199a-3p, its corresponding anti-miRNA, or short hairpin RNA against Cables1 were transfected into cells. The proliferation of cardiac c-kit⁺ cells was evaluated using EdU and flow cytometry. Furthermore, we examined cell apoptosis by flow cytometry under treatment with 200nM angiotensin II for 48 h. The levels of miR199a-3p and Cables1 mRNA were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Western blot was performed to examine the expression of Cables1 and P53 proteins.

Results

We demonstrated a significantly decreased expression of miR199a-3p in heart failure samples compared with healthy donors. Meanwhile, we identified miR199a-3p as a proliferation- and apoptosis-associated regulator impacted through Cdk5 and Abl enzyme substrate 1 (CABLES1) targeting, and also attributed their repression to P53 protein expression. We further demonstrated that P53 induced miR199a-3p expression and, in turn, miR199-3p decreased P53 activity.

Conclusion

Collectively, our findings uncover one new mechanism by which P53 induced miR199a-3p expression and, in turn, miR199-3p decreased P53 activity. Therefore, miR199a-3p and P53 are coupled through CABLES1 and comprise a novel negative feedback loop that likely contributes to cardiac c-kit⁺ cell proliferation and apoptosis.

Sudden cardiac death in a patient with advanced hepatocellular carcinoma with good response to sorafenib treatment: A case report with literature analysis

Hepatocellular carcinoma (HCC) is the principal primary liver tumor, representing the third largest cause of cancer-associated death worldwide. The actual reference standard systemic treatment for advanced HCC is represented by sorafenib, a multi-targeted orally active small-molecule tyrosine kinase inhibitor. Sorafenib has exhibited a good general safety profile in multiple clinical trials. However, adverse drug-associated events are common, occasionally severe, and special attention should be paid to cardiovascular adverse events, particularly in patients with risk factors or known heart disease. In the present study, the case of a patient with no known cardiovascular risk factors affected by highly enhancing advanced HCC in cirrhotic liver, who died during successful sorafenib monotherapy, is reported.

Endothelin-1 promotes hypertrophic remodelling of cardiac myocytes by activating sustained signalling and transcription downstream of endothelin type A receptors

G-protein coupled receptor (GPCR) mediated activation of the MAPK signalling cascade is a key pathway in the induction of hypertrophic remodelling of the heart – a response to pathological cues including hypertension and myocardial infarction. While levels of pro-hypertrophic hormone agonists of GPCRs increase during periods of greater workload to enhance cardiac output, hypertrophy does not necessarily result. Here we investigated the relationship between the duration of exposure to the pro-hypertrophic GPCR agonist endothelin-1 (ET-1) and the induction of hypertrophic remodelling in neonatal rat ventricular myocytes (NRVM) and in the adult rat heart in vivo. Notably, a 15 min pulse of ET-1 was sufficient to induce markers of hypertrophy that were present when measured at 24 h in vivo and 48 h in vitro. The persistence of ET-1 action was insensitive to ET type A receptor (ET_A receptor) antagonism with BQ123. The extended effects of ET-1 were dependent upon sustained MAPK signalling and involved persistent transcription. Inhibitors of endocytosis however conferred sensitivity upon the hypertrophic response to BQ123, suggesting that endocytosis of ET_A receptors following ligand binding preserves their active state by protection against antagonist. Contrastingly, α₁ adrenergic-induced hypertrophic responses required the continued presence of agonist and were sensitive to antagonist. These studies shed new light on strategies to pharmacologically intervene in the action of different pro-hypertrophic mediators.

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Acute ET-1 exposure elicits a long-lasting cardiac myocyte hypertrophic response.

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ET-1 effects depend on persistent MAPK signalling and active transcription.

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ET-1 elicited hypertrophy is insensitive to subsequent ET_A receptor antagonism.

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Endocytosis inhibition potentiates ET-1-induction of hypertrophy markers.

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Endocytosis inhibition sensitises effects of ET-1 to ET_A receptor antagonist.

TSC-22 up-regulates collagen 3a1 gene expression in the rat heart

BACKGROUND

The transforming growth factor (TGF)-β is one of the key mediators in cardiac remodelling occurring after myocardial infarction (MI) and in hypertensive heart disease. The TGF-β-stimulated clone 22 (TSC-22) is a leucine zipper protein expressed in many tissues and possessing various transcription-modulating activities. However, its function in the heart remains unknown.

METHODS

The aim of the present study was to characterize cardiac TSC-22 expression in vivo in cardiac remodelling and in myocytes in vitro. In addition, we used TSC-22 gene transfer in order to examine the effects of TSC-22 on cardiac gene expression and function.

RESULTS

We found that TSC-22 is rapidly up-regulated by multiple hypertrophic stimuli, and in post-MI remodelling both TSC-22 mRNA and protein levels were up-regulated (4.1-fold, P <0.001 and 3.0-fold, P <0.05, respectively) already on day 1. We observed that both losartan and metoprolol treatments reduced left ventricular TSC-22 gene expression. Finally, TSC-22 overexpression by local intramyocardial adenovirus-mediated gene delivery showed that TSC-22 appears to have a role in regulating collagen type IIIα1 gene expression in the heart.

CONCLUSIONS

These results demonstrate that TSC-22 expression is induced in response to cardiac overload. Moreover, our data suggests that, by regulating collagen expression in the heart in vivo, TSC-22 could be a potential target for fibrosis-preventing therapies.

KeyGenes, a Tool to Probe Tissue Differentiation Using a Human Fetal Transcriptional Atlas

Differentiated derivatives of human pluripotent stem cells in culture are generally phenotypically immature compared to their adult counterparts. Their identity is often difficult to determine with certainty because little is known about their human fetal equivalents in vivo. Cellular identity and signaling pathways directing differentiation are usually determined by extrapolating information from either human adult tissue or model organisms, assuming conservation with humans. To resolve this, we generated a collection of human fetal transcriptional profiles at different developmental stages. Moreover, we developed an algorithm, KeyGenes, which uses this dataset to quantify the extent to which next-generation sequencing or microarray data resemble specific cell or tissue types in the human fetus. Using KeyGenes combined with the human fetal atlas, we identified multiple cell and tissue samples unambiguously on a limited set of features. We thus provide a flexible and expandable platform to monitor and evaluate the efficiency of differentiation in vitro.

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NGS-derived transcriptional profiles of human fetal tissues/organs are generated

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Algorithm called KeyGenes uses a training set to predict the identity of a test set

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KeyGenes using the fetal atlas identifies NGS- and microarray-derived data

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KeyGenes is a flexible and expandable platform to monitor stem cell differentiations

Gene expression network analysis reveals new transcriptional regulators as novel factors in human ischemic cardiomyopathy

BACKGROUND

Ischemic cardiomyopathy (ICM) is characterized by transcriptomic changes that alter cellular processes leading to decreased cardiac output. Because the molecular network of ICM is largely unknown, the aim of this study was to characterize the role of new transcriptional regulators in the molecular mechanisms underlying the responses to ischemia.

METHODS

Myocardial tissue explants from ICM patients and control (CNT) subjects were analyzed by RNA-Sequencing (RNA-Seq) and quantitative Real-Time PCR.

RESULTS

Enrichment analysis of the ICM transcriptomic profile allowed the characterization of novel master regulators. We found that the expression of the transcriptional regulators SP100 (-1.5-fold, p < 0.05), CITED2 (-3.8-fold, p < 0.05), CEBPD (-4.9-fold, p < 0.05) and BCL3 (-3.3-fold, p < 0.05) were lower in ICM than in CNT. To gain insights into the molecular network defined by the transcription factors, we identified CEBPD, BCL3, and HIF1A target genes in the RNA-Seq datasets. We further characterized the biological processes of the target genes by gene ontology annotation. Our results suggest that CEBPD-inducible genes with roles in the inhibition of apoptosis are downregulated and that BCL3-repressible genes are involved in the regulation of cellular metabolism in ICM. Moreover, our results suggest that CITED2 downregulation causes increased expression of HIF1A target genes. Functional analysis of HIF1A target genes revealed that hypoxic and stress response genes are activated in ICM. Finally, we found a significant correlation between the mRNA levels of BCL3 and the mRNA levels of both CEBPD (r = 0.73, p < 0.001) and CITED2 (r = 0.56, p < 0.05). Interestingly, CITED2 mRNA levels are directly related to ejection fraction (EF) (r = 0.54, p < 0.05).

CONCLUSIONS

Our data indicate that changes in the expression of SP100, CITED2, CEBPD, and BCL3 affect their transcription regulatory networks, which subsequently alter a number of biological processes in ICM patients. The relationship between CITED2 mRNA levels and EF emphasizes the importance of this transcription factor in ICM. Moreover, our findings identify new mechanisms used to interpret gene expression changes in ICM and provide valuable resources for further investigation of the molecular basis of human cardiac ischemic response.

Emerging roles of junctophilin-2 in the heart and implications for cardiac diseases

Cardiomyocytes rely on a highly specialized subcellular architecture to maintain normal cardiac function. In a little over a decade, junctophilin-2 (JPH2) has become recognized as a cardiac structural protein critical in forming junctional membrane complexes (JMCs), which are subcellular domains essential for excitation-contraction coupling within the heart. While initial studies described the structure of JPH2 and its role in anchoring junctional sarcoplasmic reticulum and transverse-tubule (T-tubule) membrane invaginations, recent research has an expanded role of JPH2 in JMC structure and function. For example, JPH2 is necessary for the development of postnatal T-tubule in mammals. It is also critical for the maintenance of the complex JMC architecture and stabilization of local ion channels in mature cardiomyocytes. Loss of this function by mutations or down-regulation of protein expression has been linked to hypertrophic cardiomyopathy, arrhythmias, and progression of disease in failing hearts. In this review, we summarize current views on the roles of JPH2 within the heart and how JPH2 dysregulation may contribute to a variety of cardiac diseases.

Crosstalk between mitogen-activated protein kinases and mitochondria in cardiac diseases: therapeutic perspectives

Cardiovascular diseases cause more mortality and morbidity worldwide than any other diseases. Although many intracellular signaling pathways influence cardiac physiology and pathology, the mitogen-activated protein kinase (MAPK) family has garnered significant attention because of its vast implications in signaling and crosstalk with other signaling networks. The extensively studied MAPKs ERK1/2, p38, JNK, and ERK5, demonstrate unique intracellular signaling mechanisms, responding to a myriad of mitogens and stressors and influencing the signaling of cardiac development, metabolism, performance, and pathogenesis. Definitive relationships between MAPK signaling and cardiac dysfunction remain elusive, despite 30 years of extensive clinical studies and basic research of various animal/cell models, severities of stress, and types of stimuli. Still, several studies have proven the importance of MAPK crosstalk with mitochondria, powerhouses of the cell that provide over 80% of ATP for normal cardiomyocyte function and play a crucial role in cell death. Although many questions remain unanswered, there exists enough evidence to consider the possibility of targeting MAPK-mitochondria interactions in the prevention and treatment of heart disease. The goal of this review is to integrate previous studies into a discussion of MAPKs and MAPK-mitochondria signaling in cardiac diseases, such as myocardial infarction (ischemia), hypertrophy and heart failure. A comprehensive understanding of relevant molecular mechanisms, as well as challenges for studies in this area, will facilitate the development of new pharmacological agents and genetic manipulations for therapy of cardiovascular diseases.

Desmin modifications associate with amyloid-like oligomers deposition in heart failure

AIMS

The ultimate cause of heart failure (HF) is not known to date. The cytoskeletal protein desmin is differentially modified and forms amyloid-like oligomers in HF. We postulated that desmin post-translational modifications (PTMs) could drive aberrant desmin aggregation in HF. Therefore, we identified these PTMs and investigated their impact on desmin amyloidogenicity in human and experimental HF.

METHODS AND RESULTS

We detected increased levels of selectively phosphorylated and cleaved desmin in a canine pacing model of dyssynchronous HF (DHF) compared with either controls or animals treated with cardiac resynchronization therapy (CRT). This unique animal model combines clinically relevant features with the possibility of a partly rescued phenotype. We confirmed analogous changes in desmin modifications in human HF and identified two phosphorylation sites within a glycogen synthase kinase 3 (GSK3) consensus sequence. Desmin-positive oligomers were also increased in DHF hearts compared with controls. Their amyloid properties were decreased by treatment with CRT or an anti-amyloid small molecule. Finally, we confirmed GSK3's involvement with desmin phosphorylation using an in vitro model.

CONCLUSIONS

Based on these findings, we postulate a new mechanism of cardiac toxicity based on the PTM-driven accumulation of desmin amyloid-like oligomers. Phosphorylation and cleavage as well as oligomers formation are reduced by treatment (CRT) indicating a relationship between the three. Finally, the decrease of desmin amyloid-like oligomers with CRT or small molecules points both to a general mechanism of HF based on desmin toxicity that is independent of protein mutations and to novel potential therapies.

LIF and the heart: just another brick in the wall?

Multiple studies have shown that the cytokine leukemia inhibitory factor (LIF) is protective of the myocardium in the acute stress of ischemia-reperfusion. All three major intracellular signaling pathways that are activated by LIF in cardiac myocytes have been linked to actions that protect against oxidative stress and cell death, either at the level of the mitochondrion or via nuclear transcription. In addition, LIF has been shown to contribute to post-myocardial infarction cardiac repair and regeneration, by stimulating the homing of bone marrow-derived cardiac progenitors to the injured myocardium, the differentiation of resident cardiac stem cells into endothelial cells, and neovascularization. Whether LIF offers protection to the heart under chronic stress such as hypertension-induced cardiac remodeling and heart failure is not known. However, mice with cardiac myocyte restricted knockout of STAT3, a principal transcription factor activated by LIF, develop heart failure with age, and cardiac STAT3 levels are reported to be decreased in heart failure patients. In addition, endogenously produced LIF has been implicated in the cholinergic transdiffrentiation that may serve to attenuate sympathetic overdrive in heart failure and in the peri-infarct region of the heart after myocardial infarction. Surprisingly, therapeutic strategies to exploit the beneficial actions of LIF on the injured myocardium have received scant attention. Nor is it established whether the purported so-called adverse effects of LIF observed in isolated cardiac myocytes have physiological relevance in vivo. Here we present an overview of the actions of LIF in the heart with the goal of stimulating further research into the translational potential of this pleiotropic cytokine.

The AP-1 transcription factor c-Jun prevents stress-imposed maladaptive remodeling of the heart

Systemic hypertension increases cardiac workload and subsequently induces signaling networks in heart that underlie myocyte growth (hypertrophic response) through expansion of sarcomeres with the aim to increase contractility. However, conditions of increased workload can induce both adaptive and maladaptive growth of heart muscle. Previous studies implicate two members of the AP-1 transcription factor family, junD and fra-1, in regulation of heart growth during hypertrophic response. In this study, we investigate the function of the AP-1 transcription factors, c-jun and c-fos, in heart growth. Using pressure overload-induced cardiac hypertrophy in mice and targeted deletion of Jun or Fos in cardiomyocytes, we show that c-jun is required for adaptive cardiac hypertrophy, while c-fos is dispensable in this context. c-jun promotes expression of sarcomere proteins and suppresses expression of extracellular matrix proteins. Capacity of cardiac muscle to contract depends on organization of principal thick and thin filaments, myosin and actin, within the sarcomere. In line with decreased expression of sarcomere-associated proteins, Jun-deficient cardiomyocytes present disarrangement of filaments in sarcomeres and actin cytoskeleton disorganization. Moreover, Jun-deficient hearts subjected to pressure overload display pronounced fibrosis and increased myocyte apoptosis finally resulting in dilated cardiomyopathy. In conclusion, c-jun but not c-fos is required to induce a transcriptional program aimed at adapting heart growth upon increased workload.

Unrestrained p38 MAPK activation in Dusp1/4 double-null mice induces cardiomyopathy

RATIONALE

Mitogen-activated protein kinases (MAPKs) are activated in the heart by disease-inducing and stress-inducing stimuli, where they participate in hypertrophy, remodeling, contractility, and heart failure. A family of dual-specificity phosphatases (DUSPs) directly inactivates each of the MAPK terminal effectors, potentially serving a cardioprotective role.

OBJECTIVE

To determine the role of DUSP1 and DUSP4 in regulating p38 MAPK function in the heart and the effect on disease.

METHODS AND RESULTS

Here, we generated mice and mouse embryonic fibroblasts lacking both Dusp1 and Dusp4 genes. Although single nulls showed no molecular effects, combined disruption of Dusp1/4 promoted unrestrained p38 MAPK activity in both mouse embryonic fibroblasts and the heart, with no change in the phosphorylation of c-Jun N-terminal kinases or extracellular signal-regulated kinases at baseline or with stress stimulation. Single disruption of either Dusp1 or Dusp4 did not result in cardiac pathology, although Dusp1/4 double-null mice exhibited cardiomyopathy and increased mortality with aging. Pharmacological inhibition of p38 MAPK with SB731445 ameliorated cardiomyopathy in Dusp1/4 double-null mice, indicating that DUSP1/4 function primarily through p38 MAPK in affecting disease. At the cellular level, unrestrained p38 MAPK activity diminished cardiac contractility and Ca2+ handling, which was acutely reversed with a p38 inhibitory compound. Poor function in Dusp1/4 double-null mice also was partially rescued by phospholamban deletion.

CONCLUSIONS

Our data demonstrate that Dusp1 and Dusp4 are cardioprotective genes that play a critical role in the heart by dampening p38 MAPK signaling that would otherwise reduce contractility and induce cardiomyopathy.

Alterations in the contractile phenotype of the bladder: lessons for understanding physiological and pathological remodelling of smooth muscle

The contractile properties of the urinary bladder are changed by the conditions of normal development and partial bladder outlet obstruction. This change in the contractile phenotype is accompanied by changes in the regulatory cascades and filaments that regulate contractility. This review focuses on such changes during the course of normal development and in response to obstruction. Our goal is to discuss the experimental evidence that has accumulated from work in animal models and correlate these findings with the human voiding phenotype.

In search of novel targets for heart disease: myocardin and myocardin-related transcriptional cofactors

Growing evidence suggests that gene-regulatory networks, which are responsible for directing cardiovascular development, are altered under stress conditions in the adult heart. The cardiac gene regulatory network is controlled by cardioenriched transcription factors and multiple-cell-signaling inputs. Transcriptional coactivators also participate in gene-regulatory circuits as the primary targets of both physiological and pathological signals. Here, we focus on the recently discovered myocardin-(MYOCD) related family of transcriptional cofactors (MRTF-A and MRTF-B) which associate with the serum response transcription factor and activate the expression of a variety of target genes involved in cardiac growth and adaptation to stress via overlapping but distinct mechanisms. We discuss the involvement of MYOCD, MRTF-A, and MRTF-B in the development of cardiac dysfunction and to what extent modulation of the expression of these factors in vivo can correlate with cardiac disease outcomes. A close examination of the findings identifies the MYOCD-related transcriptional cofactors as putative therapeutic targets to improve cardiac function in heart failure conditions through distinct context-dependent mechanisms. Nevertheless, we are in support of further research to better understand the precise role of individual MYOCD-related factors in cardiac function and disease, before any therapeutic intervention is to be entertained in preclinical trials.

Combined deep microRNA and mRNA sequencing identifies protective transcriptomal signature of enhanced PI3Kα signaling in cardiac hypertrophy

The perturbation of myocardial transcriptome homeostasis is the hallmark of pathological hypertrophy, underlying the maladaptive myocardial remodeling secondary to pathological stresses. Classic and novel therapeutics that provide beneficial effects against pathological remodeling likely impact myocardial transcriptome architecture, including miRNA and mRNA expression profiles. Microarray and PCR-based technologies, although employed extensively, cannot provide adequate sequence coverage or quantitative accuracy to test this hypothesis directly. The goal of this study was to develop and exploit next-generation sequencing approaches for comprehensive and quantitative analyses of myocardial miRNAs and mRNAs to test the hypothesis that augmented phosphoinositide-3-kinase-p110α (PI3Kα) signaling in the setting of pathological hypertrophy provides beneficial effects through remodeling of the myocardial transcriptome signature. In these studies, a molecular and bioinformatic pipeline permitting comprehensive analysis and quantification of myocardial miRNA and mRNA expression with next-generation sequencing was developed and the impact of enhanced PI3Kα signaling on the myocardial transcriptome signature of pressure overload-induced pathological hypertrophy was explored. These analyses identified multiple miRNAs and mRNAs that were abnormally expressed in pathological hypertrophy and partially or completely normalized with increased PI3Kα signaling. Additionally, several novel miRNAs potentially linked to remodeling in cardiac hypertrophy were identified. Additional experiments revealed that increased PI3Kα signaling reduces cardiac fibrosis in pathological hypertrophy through modulating TGF-β signaling and miR-21 expression. In conclusion, using the approach of combined miRNA and mRNA sequencing, we identify the protective transcriptome signature of enhanced PI3Kα signaling in the context of pathological hypertrophy, and demonstrate the regulation of TGF-β/miR-21 by which enhanced PI3Kα signaling protects against cardiac fibrosis.

PPAR-gamma in the Cardiovascular System

Peroxisome proliferator-activated receptor-γ (PPAR-γ), an essential transcriptional mediator of adipogenesis, lipid metabolism, insulin sensitivity, and glucose homeostasis, is increasingly recognized as a key player in inflammatory cells and in cardiovascular diseases (CVD) such as hypertension, cardiac hypertrophy, congestive heart failure, and atherosclerosis. PPAR-γ agonists, the thiazolidinediones (TZDs), increase insulin sensitivity, lower blood glucose, decrease circulating free fatty acids and triglycerides, lower blood pressure, reduce inflammatory markers, and reduce atherosclerosis in insulin-resistant patients and animal models. Human genetic studies on PPAR-γ have revealed that functional changes in this nuclear receptor are associated with CVD. Recent controversial clinical studies raise the question of deleterious action of PPAR-γ agonists on the cardiovascular system. These complex interactions of metabolic responsive factors and cardiovascular disease promise to be important areas of focus for the future.

IQGAP1 regulates ERK1/2 and AKT signalling in the heart and sustains functional remodelling upon pressure overload

AIMS

The Raf-MEK1/2-ERK1/2 (ERK1/2-extracellular signal-regulated kinases 1/2) signalling cascade is crucial in triggering cardiac responses to different stress stimuli. Scaffold proteins are key elements in coordinating signalling molecules for their appropriate spatiotemporal activation. Here, we investigated the role of IQ motif-containing GTPase-activating protein 1 (IQGAP1), a scaffold for the ERK1/2 cascade, in heart function and remodelling in response to pressure overload.

METHODS AND RESULTS

IQGAP1-null mice have unaltered basal heart function. When subjected to pressure overload, IQGAP1-null mice initially develop a compensatory hypertrophy indistinguishable from that of wild-type (WT) mice. However, upon a prolonged stimulus, the hypertrophic response develops towards a thinning of left ventricular walls, chamber dilation, and a decrease in contractility, in an accelerated fashion compared with WT mice. This unfavourable cardiac remodelling is characterized by blunted reactivation of the foetal gene programme, impaired cardiomyocyte hypertrophy, and increased cardiomyocyte apoptosis. Analysis of signalling pathways revealed two temporally distinct waves of both ERK1/2 and AKT phosphorylation peaking, respectively, at 10 min and 4 days after aortic banding in WT hearts. IQGAP1-null mice show strongly impaired phosphorylation of MEK1/2-ERK1/2 and AKT following 4 days of pressure overload, but normal activation of these kinases after 10 min. Pull-down experiments indicated that IQGAP1 is able to bind the three components of the ERK cascade, namely c-Raf, MEK1/2, and ERK1/2, as well as AKT in the heart.

CONCLUSION

These data demonstrate, for the first time, a key role for the scaffold protein IQGAP1 in integrating hypertrophy and survival signals in the heart and regulating long-term left ventricle remodelling upon pressure overload.

Gene coexpression network topology of cardiac development, hypertrophy, and failure

BACKGROUND

Network analysis techniques allow a more accurate reflection of underlying systems biology to be realized than traditional unidimensional molecular biology approaches. Using gene coexpression network analysis, we define the gene expression network topology of cardiac hypertrophy and failure and the extent of recapitulation of fetal gene expression programs in failing and hypertrophied adult myocardium.

METHODS AND RESULTS

We assembled all myocardial transcript data in the Gene Expression Omnibus (n=1617). Because hierarchical analysis revealed species had primacy over disease clustering, we focused this analysis on the most complete (murine) dataset (n=478). Using gene coexpression network analysis, we derived functional modules, regulatory mediators, and higher-order topological relationships between genes and identified 50 gene coexpression modules in developing myocardium that were not present in normal adult tissue. We found that known gene expression markers of myocardial adaptation were members of upregulated modules but not hub genes. We identified ZIC2 as a novel transcription factor associated with coexpression modules common to developing and failing myocardium. Of 50 fetal gene coexpression modules, 3 (6%) were reproduced in hypertrophied myocardium and 7 (14%) were reproduced in failing myocardium. One fetal module was common to both failing and hypertrophied myocardium.

CONCLUSIONS

Network modeling allows systems analysis of cardiovascular development and disease. Although we did not find evidence for a global coordinated program of fetal gene expression in adult myocardial adaptation, our analysis revealed specific gene expression modules active during both development and disease and specific candidates for their regulation.

MicroRNA-199b targets the nuclear kinase Dyrk1a in an auto-amplification loop promoting calcineurin/NFAT signalling

MicroRNAs (miRs) are a class of single-stranded, non-coding RNAs of about 22 nucleotides in length. Increasing evidence implicates miRs in myocardial disease processes. Here we show that miR-199b is a direct calcineurin/NFAT target gene that increases in expression in mouse and human heart failure, and targets the nuclear NFAT kinase dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1a (Dyrk1a), constituting a pathogenic feed forward mechanism that affects calcineurin-responsive gene expression. Mutant mice overexpressing miR-199b, or haploinsufficient for Dyrk1a, are sensitized to calcineurin/NFAT signalling or pressure overload and show stress-induced cardiomegaly through reduced Dyrk1a expression. In vivo inhibition of miR-199b by a specific antagomir normalized Dyrk1a expression, reduced nuclear NFAT activity and caused marked inhibition and even reversal of hypertrophy and fibrosis in mouse models of heart failure. Our results reveal that microRNAs affect cardiac cellular signalling and gene expression, and implicate miR-199b as a therapeutic target in heart failure.

Integrated genomic approaches implicate osteoglycin (Ogn) in the regulation of left ventricular mass

Left ventricular mass (LVM) and cardiac gene expression are complex traits regulated by factors both intrinsic and extrinsic to the heart. To dissect the major determinants of LVM, we combined expression quantitative trait locus1 and quantitative trait transcript (QTT) analyses of the cardiac transcriptome in the rat. Using these methods and in vitro functional assays, we identified osteoglycin (Ogn) as a major candidate regulator of rat LVM, with increased Ogn protein expression associated with elevated LVM. We also applied genome-wide QTT analysis to the human heart and observed that, out of 22,000 transcripts, OGN transcript abundance had the highest correlation with LVM. We further confirmed a role for Ogn in the in vivo regulation of LVM in Ogn knockout mice. Taken together, these data implicate Ogn as a key regulator of LVM in rats, mice and humans, and suggest that Ogn modifies the hypertrophic response to extrinsic factors such as hypertension and aortic stenosis.

Proteomic profiling of endothelin-1-stimulated hypertrophic cardiomyocytes reveals the increase of four different desmin species and alpha-B-crystallin

We performed a proteomic investigation on primary cultures of neonatal rat cardiomyocytes after treatment with 10 nM endothelin-1 (ET1) for 48 h, an in vitro model for cardiac hypertrophy. Two-dimensional gel electrophoresis profiles of cell lysates were compared after colloidal Coomassie Blue staining. 12 protein spots that significantly changed in density due to ET1 stimulation were selected for in-gel digestion and identified through mass spectrometry. Of these, 8 spots were increased and 4 were decreased. Four of the increased proteins were identified as desmin, the cardiac component of intermediate filaments and one as alpha-B-crystallin, a molecular chaperone that binds desmin. All the desmins increased 2- to 5-fold, and alpha-B-crystallin increased 2-fold after ET1 treatment. Desmin cytoskeleton has been implicated in the regulation of mitochondrial activity and distribution, as well as in the formation of amyloid bodies. Mitochondria-specific fluorescent probe MitoTracker indicated mitochondrial redistribution in hypertrophic cells. An increase of amyloid aggregates containing desmin upon treatment with ET1 was detected by filter assay. Of the four proteins that showed decreased abundance after ET1 treatment, the chaperones hsp60 and grp75 were decreased 13- and 9-fold, respectively. In conclusion, proteomic profiling of ET1-stimulated rat neonatal cardiomyocytes reveals specific changes in cardiac molecular phenotype mainly involving intermediate filament and molecular chaperone proteins.

Temporal regulation of expression of immediate early and second phase transcripts by endothelin-1 in cardiomyocytes

BACKGROUND

Endothelin-1 stimulates Gq protein-coupled receptors to promote proliferation in dividing cells or hypertrophy in terminally differentiated cardiomyocytes. In cardiomyocytes, endothelin-1 rapidly (within minutes) stimulates protein kinase signaling, including extracellular-signal regulated kinases 1/2 (ERK1/2; though not ERK5), with phenotypic/physiological changes developing from approximately 12 h. Hypertrophy is associated with changes in mRNA/protein expression, presumably consequent to protein kinase signaling, but the connections between early, transient signaling events and developed hypertrophy are unknown.

RESULTS

Using microarrays, we defined the early transcriptional responses of neonatal rat cardiomyocytes to endothelin-1 over 4 h, differentiating between immediate early gene (IEG) and second phase RNAs with cycloheximide. IEGs exhibited differential temporal and transient regulation, with expression of second phase RNAs within 1 h. Of transcripts upregulated at 30 minutes encoding established proteins, 28 were inhibited >50% by U0126 (which inhibits ERK1/2/5 signaling), with 9 inhibited 25-50%. Expression of only four transcripts was not inhibited. At 1 h, most RNAs (approximately 67%) were equally changed in total and polysomal RNA with approximately 17% of transcripts increased to a greater extent in polysomes. Thus, changes in expression of most protein-coding RNAs should be reflected in protein synthesis. However, approximately 16% of transcripts were essentially excluded from the polysomes, including some protein-coding mRNAs, presumably inefficiently translated.

CONCLUSION

The phasic, temporal regulation of early transcriptional responses induced by endothelin-1 in cardiomyocytes indicates that, even in terminally differentiated cells, signals are propagated beyond the primary signaling pathways through transcriptional networks leading to phenotypic changes (that is, hypertrophy). Furthermore, ERK1/2 signaling plays a major role in this response.

Mechanical stress-strain sensors embedded in cardiac cytoskeleton: Z disk, titin, and associated structures

Cardiac muscle is equipped with intricate intrinsic mechanisms to regulate adaptive remodeling. Recent and extensive experimental findings powered by novel strategies for screening protein-protein interactions, improved imaging technologies, and versatile transgenic mouse methodologies reveal that Z disks and titin filaments possess unexpectedly complicated sensory and modulatory mechanisms for signal reception and transduction. These mechanisms employ molecules such as muscle-enriched LIM domain proteins, PDZ-LIM domain proteins, myozenin gene family members, titin-associated ankyrin repeat family proteins, and muscle-specific ring finger proteins, which have been identified as potential molecular sensor components. Moreover, classic transmembrane signaling processes, including mitogen-activated kinase, protein kinase C, and calcium signaling, also involve novel interactions with the Z disk/titin network. This compartmentalization of signaling complexes permits alteration of receptor-dependent transcriptional regulation by direct sensing of intrinsic stress. Newly identified mechanical stress sensors are not limited to Z-disk region and to I-band and M-band regions of titin but are also embedded in muscle-specific membrane systems such as the costamere, intercalated disks, and caveolae-like microdomains. This review summarizes current knowledge of this rapidly developing area with focus on how the heart adjusts physiological remodeling process to meet with mechanical demands and how this process fails in cardiac pathologies.

Comparison of Gene Expression Profiling in Pressure and Volume Overload-Induced Myocardial Hypertrophies in Rats

Gene expression profiling has been conducted in rat hearts subjected to pressure overload (PO). However, pressure and volume overload produce morphologically and functionally distinct forms of cardiac hypertrophy. Surprisingly, gene expression profiling has not been reported for in an animal model of volume overload (VO). We therefore compared the gene expression profiles in the hypertrophied myocardium of rats subjected to PO and VO using DNA chip technology (Affymetrix U34A). Constriction of the abdominal aorta and abdominal aortocaval shunting were used to induce PO and VO, respectively. The gene expression profiles of the left ventricle (LV) 4 weeks after the procedure were analyzed by DNA chips. There were comparable increases in the left ventricular weight/body weight ratio in rats subjected to PO and VO. Echocardiography revealed concentric hypertrophy in the PO animals, but eccentric hypertrophy in the rats subjected to VO. The expressions of many genes were altered in VO, PO, or both. Among the genes that were upregulated in both forms of hypertrophy, greatly increased expressions of B-type natriuretic peptide, lysyl oxidase-like protein 1 and metallothionein-1 (MT) were confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR). Because free radicals are increased in the hypertrophied heart and may contribute to apoptosis, we examined the role of MT, a free radical scavenger, in apoptosis. The over-expression of MT in H9c2 cells inhibited norepinephrine-induced apoptosis, suggesting that MT may act as an anti-apoptotic molecule in cardiac hypertrophy. In conclusion, we found that many genes were regulated in VO, PO, or both. In addition, a novel role of MT in the hypertrophied myocardium was suggested.

Disruption of coordinated cardiac hypertrophy and angiogenesis contributes to the transition to heart failure

Although increased external load initially induces cardiac hypertrophy with preserved contractility, sustained overload eventually leads to heart failure through poorly understood mechanisms. Here we describe a conditional transgenic system in mice characterized by the sequential development of adaptive cardiac hypertrophy with preserved contractility in the acute phase and dilated cardiomyopathy in the chronic phase following the induction of an activated Akt1 gene in the heart. Coronary angiogenesis was enhanced during the acute phase of adaptive cardiac growth but reduced as hearts underwent pathological remodeling. Enhanced angiogenesis in the acute phase was associated with mammalian target of rapamycin-dependent induction of myocardial VEGF and angiopoietin-2 expression. Inhibition of angiogenesis by a decoy VEGF receptor in the acute phase led to decreased capillary density, contractile dysfunction, and impaired cardiac growth. Thus, both heart size and cardiac function are angiogenesis dependent, and disruption of coordinated tissue growth and angiogenesis in the heart contributes to the progression from adaptive cardiac hypertrophy to heart failure.

Structural basis of ventricular remodeling: role of the myocyte

Structural remodeling plays a major role in the progression of various heart diseases to congestive heart failure (CHF). Major contributors to this remodeling process in the heart include alterations in myocyte shape, myocyte number, and extracellular matrix. However, it is unclear as to which of these changes is most critical in the development of CHF, and this may vary by etiology. Myocyte shape alterations largely underlie the increase in chamber diameter/wall thickness characteristic of CHF. This review mainly focuses on the role of myocyte shape in ventricular remodeling. Several signaling molecules have been implicated in this process. As we learn more about the components of myocardial remodeling, new strategies to combat the progression of heart disease should arise.

Differential activation of stress-response signaling in load-induced cardiac hypertrophy and failure

Hypertrophic growth of the myocardium occurs in most forms of heart failure and may contribute to the pathogenesis of the failure state. Little is known about the regulatory mechanisms governing the often-coexisting phenotypes of hypertrophy, systolic failure, and diastolic stiffness that characterize clinical disease. We hypothesized that intracellular signaling pathways are differentially activated by graded degrees of hemodynamic stress. To test this, we developed models of graded pressure stress in mice and used them to directly compare compensated hypertrophy and pressure-overload heart failure. Surgical interventions were designed to be similar, on either side of a threshold separating compensated from decompensated responses. Our findings revealed two dramatically different hypertrophic phenotypes with only modest differences in the activation of relevant intracellular signaling pathways. Furthermore, we uncovered a functional requirement of calcineurin signaling in each model such that calcineurin suppression blunted hypertrophic growth. Remarkably, in each case, suppression of calcineurin signaling was not associated with clinical deterioration or increased mortality. Profiles of stress-response signaling and Ca2+ handling differ between the steady-state, maintenance phases of load-induced cardiac hypertrophy and failure. This information may be useful in identifying novel targets of therapy in chronic disease.

Chronic phospholamban inhibition prevents progressive cardiac dysfunction and pathological remodeling after infarction in rats

Ablation or inhibition of phospholamban (PLN) has favorable effects in several genetic murine dilated cardiomyopathies, and we showed previously that a pseudophosphorylated form of PLN mutant (S16EPLN) successfully prevented progressive heart failure in cardiomyopathic hamsters. In this study, the effects of PLN inhibition were examined in rats with heart failure after myocardial infarction (MI), a model of acquired disease. S16EPLN was delivered into failing hearts 5 weeks after MI by transcoronary gene transfer using a recombinant adeno-associated virus (rAAV) vector. In treated (MI-S16EPLN, n = 16) and control (MI-saline, n = 18) groups, infarct sizes were closely matched and the left ventricle was similarly depressed and dilated before gene transfer. At 2 and 6 months after gene transfer, MI-S16EPLN rats showed an increase in left ventricular (LV) ejection fraction and a much smaller rise in LV end-diastolic volume, compared with progressive deterioration of LV size and function in MI-saline rats. Hemodynamic measurements at 6 months showed lower LV end-diastolic pressures, with enhanced LV function (contractility and relaxation), lowered LV mass and myocyte size, and less fibrosis in MI-S16EPLN rats. Thus, PLN inhibition by in vivo rAAV gene transfer is an effective strategy for the chronic treatment of an acquired form of established heart failure.

Disruption of the nonneuronal tph1 gene demonstrates the importance of peripheral serotonin in cardiac function

Serotonin (5-HT) controls a wide range of biological functions. In the brain, its implication as a neurotransmitter and in the control of behavioral traits has been largely documented. At the periphery, its modulatory role in physiological processes, such as the cardiovascular function, is still poorly understood. The rate-limiting enzyme of 5-HT synthesis, tryptophan hydroxylase (TPH), is encoded by two genes, the well characterized tph1 gene and a recently identified tph2 gene. In this article, based on the study of a mutant mouse in which the tph1 gene has been inactivated by replacement with the beta-galactosidase gene, we establish that the neuronal tph2 is expressed in neurons of the raphe nuclei and of the myenteric plexus, whereas the nonneuronal tph1, as detected by beta-galactosidase expression, is in the pineal gland and the enterochromaffin cells. Anatomic examination of the mutant mice revealed larger heart sizes than in wild-type mice. Histological investigation indicates that the primary structure of the heart muscle is not affected. Hemodynamic analyses demonstrate abnormal cardiac activity, which ultimately leads to heart failure of the mutant animals. This report links loss of tph1 gene expression, and thus of peripheral 5-HT, to a cardiac dysfunction phenotype. The tph1-/- mutant may be valuable for investigating cardiovascular dysfunction observed in heart failure in humans.

Heart failure -- a challenge to our current concepts of excitation-contraction coupling

Development of novel therapeutic strategies for congestive heart failure (CHF) seems to be hampered by insufficient knowledge of the molecular machinery of excitation-contraction (EC) coupling in both normal and failing hearts. Cardiac hypertrophy and failure represent a multitude of cardiac phenotypes, and available invasive and non-invasive techniques, briefly reviewed here, allow proper quantification of myocardial function in experimental models even in rats and mice. Both reduced fractional shortening and reduced velocity of contraction characterize myocardial failure. Only when myocardial function is depressed in vivo can meaningful studies be done in vitro of contractility and EC coupling. Also, we point out potential limitations with the whole cell patch clamp technique. Two main factors stand out as explanations for myocardial failure. First, a basic feature of CHF seems to be a reduced Ca(2+) load of the sarcoplasmic reticulum (SR) mainly due to a low phosphorylation level of phospholamban. Second, there seems to be a defect of the trigger mechanism of Ca(2+) release from the SR. We argue that this defect only becomes manifest in the presence of reduced Ca(2+) reuptake capacity of the SR and that it may not be solely attributable to reduced gain of the Ca(2+)-induced Ca(2+) release (CICR). We list several possible explanations for this defect that represent important avenues for future research.